This invention relates to an operation control system for controlling the operation of internal combustion engines at and after starting, and more particularly to an operation control system of this kind, which is intended to enhance the startability of the engine of a high output type when the engine temperature is low at and after the start of the engine.
Conventional starting control systems for internal combustion engines are generally constructed such that at the start of the engine, the opening of an intake air amount control valve is set to a value dependent on the engine temperature to obtain a required amount of intake air, and the amount of fuel is also set to a value dependent on the engine temperature, whereby a predetermined air-fuel mixture is supplied to the engine.
According to the conventional starting control systems, the opening of the control valve is set to a larger value as the engine temperature is lower, which however, causes degraded startability of engines of some types. More specifically, there are some engines which have fuel injection systems, and which have their intake valves, exhaust valves and throttle valves enlarged in diameter to increase the engine output in order to meet the recent demand for more versatile vehicles.
In an engine with such enlarged intake valves, exhaust valves and throttle valves, intake air flow in the intake pipe is slow in speed, which causes degraded atomization of fuel. Especially when the engine temperature is low, as described above, the intake air amount control valve is set to a large opening, so that vacuum created within the intake pipe becomes lower, resulting in further degraded atomization of fuel. Further, in a low intake air flow region such as at the start of the engine, the valve-overlapping period when the intake and exhaust valves are simultaneously open is so long that a large amount of intake air drawn into the cylinder is discharged into the exhaust pipe through the exhaust valve directly from the intake valve. Therefore, the startability is further degraded.
Moreover, if a vacuum-responsive type ignition timing control device is employed in combination with the above described starting control system in which the opening of the control valve is set to a larger value as the engine temperature is lower, it is difficult to properly control the ignition timing, since vacuum sufficient to achieve proper ignition timing control cannot be created especially when the engine temperature is low, thus being unable to meet the requirement that the ignition timing should be advanced by a larger amount as the engine temperature is lower. This also forms a factor for degraded startability of the engine.